Skin cancer is the most common type of cancer in the United States. An estimated 40 to 50 percent of Americans who live to age 65 will have skin cancer at least once. The most common skin cancer is basal cell carcinoma, which accounts for more than 90 percent of all skin cancers in the United States.

The most virulent form of skin cancer is melanoma. In some parts of the world, especially in Western countries, the number of people who develop melanoma is increasing faster than any other cancer. In the United States, for example, the number of new cases of melanoma has more than doubled in the past 20 years.

What are the most common forms of skin cancer?

Three types of skin cancer are the most common:

Basal cell carcinoma is a slow-growing cancer that seldom spreads to other parts of the body. Basal cells, which are round, form the layer just underneath the epidermis, or outer layer of the skin.

Squamous cell carcinoma spreads more often than basal cell carcinoma, but still is considered rare. Squamous cells, which are flat, make up most of the epidermis.

Melanoma is the most serious type of skin cancer. It occurs when melanocytes, the pigment cells in the lower part of the epidermis, become malignant, meaning that they start dividing uncontrollably. If melanoma spreads to the lymph nodes it may also reach other parts of the body, such as the liver, lungs or brain. In such cases, the disease is called metastatic melanoma.

What are the symptoms of skin cancer?

The most commonly noticed symptom of skin cancer is a change on the skin, especially a new growth or a sore that doesn't heal. Both basal and squamous cell cancers are found mainly on areas of the skin that are exposed to the sun - the head, face, neck, hands and arms. However, skin cancer can occur anywhere.

For melanoma, the first sign often is a change in the size, shape, color or feel of an existing mole. Melanomas can vary greatly in the way they look, but generally show one or more of the "ABCD" features:

What do we know about the causes and heredity of skin cancer?

Ultraviolet (UV) radiation from the sun is the main cause of skin cancer, although artificial sources of UV radiation, such as sunlamps and tanning booths, also play a role. UV radiation can damage the DNA, or genetic information, in skin cells, creating "misspellings" in their genetic code and, as a result, alter the function of those cells.

Cancers generally are caused by a combination of environmental and genetic factors. With skin cancer, the environment plays a greater role, but individuals can be born with a genetic disposition toward or vulnerability to getting cancer. The risk is greatest for people who have light-colored skin that freckles easily - often those who also have red or blond hair and blue or light-colored eyes - although anyone can get skin cancer.

Skin cancer is related to lifetime exposure to UV radiation, therefore most skin cancers appear after age 50. However, the sun's damaging effects begin at an early age. People who live in areas that get high levels of UV radiation from the sun are more likely to get skin cancer. For example, the highest rates of skin cancer are found in South Africa and Australia, areas that receive high amounts of UV radiation.

About 10 percent of all patients with melanoma have family members who also have had the disease. Research suggests that a mutation in the CDKN2 gene on chromosome 9 plays a role in this form of melanoma. Studies have also implicated genes on chromosomes 1 and 12 in cases of familial melanoma.

How is skin cancer treated?

Melanoma can be cured if it is diagnosed and treated when the tumor has not deeply invaded the skin. However, if a melanoma is not removed in its early stages, cancer cells may grow downward from the skin surface. When a melanoma becomes thick and deep, the disease often spreads to other parts of the body and is difficult to control.

Surgery is the standard treatment for melanoma, as well as other skin cancers. However, if the cancer has spread to other parts of the body, doctors may use other treatments, such as chemotherapy, immunotherapy, radiation therapy or a combination of these methods.

Portions of this page were adapted from the booklets "What You Need To Know About Skin Cancer" and "What You Need To Know About Melanoma," published by the National Cancer Institute [cancer.gov], National Institutes of Health (1998 and 1999).